Document acceptor assemblies, such as those used in the vending and gaming industries, typically store accepted banknotes or other documents in a cassette. A stacking mechanism may be incorporated in the assembly to facilitate storage of the documents in the cassette.
Various types of stackers are known, including piston-type stackers. It is generally desirable for the system to obtain confirmation that an accepted document has been stored properly in the cassette. One way to accomplish that is to verify the piston has completed its full stroke cycle and has returned to its home position. A linear or rotary encoder may be provided for that purpose. Unfortunately, the addition of such components may add substantially to the cost of the document stacker.
Another technique relies only on signals from the home sensor to determine whether the piston has completed its full stroke cycle. Although systems incorporating that technique may be simpler and less costly, they are unable to differentiate between different situations that may cause stalling of the stacker. For example, the stacker may stall either because the cassette is full or because the stacker mechanism is jammed. Preferably, an automated system should handle those situations differently because the former situation is the result of normal operation, whereas the latter situation should be detected as a fault.
More generally, it would be helpful to be able to detect various abnormal events during operation of a document stacker and to distinguish those events from expected, normal events.